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5.4 Root extractor: root
This function is primarily intended for use with
differential flowmeters that have a square law
4/20mA output. The root extractor linearises the
flow signal and enables the BA558C to display flow
and total in linear units.
To activate the square root extractor select 'root'
from the menu and press P which will reveal if the
function is 'On' or 'OFF'. If the function is set as
required, press E to return to the menu, or press
the Up or Down button to change the setting,
followed by the E button to return to the main
menu.
For reference, the following table shows the output
current from a non-linearised differential flowmeter.
% of full flow Current output mA
2.5
4.01
10.0
4.16
25.0
5.00
50.0
8.00
75.0
13.00
100.0
20.00
5.5 Resolution: rESn
This function defines the resolution of the least
significant rate display digit. Decreasing the
display resolution can improve the readability of a
noisy signal. Select 'rESn' from the menu and
press P which will reveal the current display
resolution. To change the resolution press the Up
or Down button to select 1, 2, 5 or 10 digits,
followed by the E button to return to the menu.
5.6 Position of the decimal points: d.P.
This function positions the decimal point in both
the rate and total displays.
The rate display can have up to five digits and the
decimal point may be positioned between any of
them, or omitted. The BA558C uses floating point
arithmetic so moving the position of the rate
display decimal point will affect totalisation.
Similarly the total display has eight digits and the
decimal point may be positioned between any of
them, or may be omitted.
To adjust the position of either decimal points
select 'd.P.' from the main menu and press P which
will activate both displays with one digit and the
following decimal pointof the total display flashing.
If only the least significant digit is flashing, this
indicates that the decimal point is omitted.
The position of the decimal points can be moved
by pressing the Up or Down push-buttons.
Operating the P push-button will toggle control
between the two displays. When both decimal
points have been correctly positioned press E to
return to the main menu.
If the application requires flow rate to be the
primary display i.e. shown on the large display,
the d.P. function enables the rate and total
displays to be interchanged. The rate display will
continue to have five digits but the total display will
be reduced from eight to six digits. The rate and
total annunciators will also be interchanged.
Pressing the Up and Down buttons simultaneously
will interchange the displays.
5.7 Calibration of the rate display using
an external current source: CAL
This function enables the zero and span of the rate
display to be adjusted using an external current
source such as a 4/20mA calibrator. When used
with an accurate traceable current source this is
the preferred method of calibration.
To calibrate the instrument select 'CAL' from the
main menu and press P. The indicator will display
'ZErO' which is a request for a 4mA input current.
Adjust the external current calibrator to 4.000mA
and again press P which will reveal the current
instrument zero display. For flow applications this
will usually be zero. Each digit of the rate display
can be changed by pressing the Up or Down
buttons. When the first digit is correct pressing P
will transfer control to the next digit. When all the
digits have been adjusted, press E to enter the
new zero. The indicator will display 'Ent' for a few
seconds while the information is being stored in
memory, and will then return to the 'ZErO' prompt .
To adjust the rate display at 20mA, press the Up
button which will cause the instrument to display
'SPAn'. Adjust the external current calibrator to
20.000mA and again press P which will reveal the
existing full scale display. Each digit of the rate
display can be changed by pressing the Up or
Down buttons. When the first digit is correct
pressing P will transfer control to the next digit.
The most significant digit, which can be 1 or 2, is
set by rolling over the previous digit. When all the
digits have been adjusted press E to enter the new
span. The instrument will display 'Ent' for a few
seconds while the information is being stored in
memory, and will then return to the 'SPAn' prompt.
Finally press E again to return to the main menu.
This function may also be used when calibrating a
complete loop including the flow meter.
